1. Field of the Invention:
This invention relates to a robot tracking method, and more particularly to a tracking method in robot operation on a workpiece moving in a circular trajectory.
2. Description of the Related Art:
In working on a stationary object (including various kinds of parts and a container-like mold for plastic products, hereinafter referred to workpiece) by an industrial robot, the robot is controlled according to the conventional teaching/playback method or off-line teaching method in such a manner that the operation point of the robot traces a desired path. However, in the process line in a factory, for example, it is often desirable to use a conveyer for conveying the workpiece, while the robot is carrying out an operation on it, in view of the working efficiency. These operations of the robot is exemplified by painting, marking, pouring liquid and mechanical processes over the workpiece placed on the conveyer.
In such a case, if the robot position (the operation point of the robot) taught when the workpiece remains stationary is simply played back without any conversion, it is impossible to move the robot along a desired path. Consequently, the tracking cannot be performed until after the trajectory of the robot has been corrected in accordance with the movement of the workpiece.
Most of the conveyers to be used in process lines in factories are of the linear traveling type or the rotary disc type. In the case using the former type, the amount of movement of the conveyer is measured by the pulse encoder, and according to the measured amount of angular movement, a coordinate system used in teaching is shifted in parallel. On the basis of the shifted coordinate system, the operation of the robot is played back, maintaining the mutual positional relationship between the workpiece and the coordinate system.